The invention relates to a stripping finger for use electrophotographic apparatus such as a copying machine and a laser beam printer. The stripping finger strips a paper from rollers, especially a fixing roller which requires a heat resistant property.
A plurality of rollers is provided in an electrophotographic apparatus such as a copying machine, a laser beam printer, and the like to develop an electrostatic latent image formed on a photosensitive drum onto a sheet of paper, using toner and then fix the toner image to the paper. The photosensitive drum and an oil-applying roller are provided at a development section of the electrophotographic apparatus, except an electrophotographic apparatus of dry type. A fixing roller and a pressure roller are provided at a fixing section thereof. A stripping finger is provided on each of the photosensitive drum, the fixing roller, and the pressure roller to smoothly discharge the paper without the paper being caught by them.
The stripping finger scoops the end of the paper with its tip in contact with the peripheral surface of the fixing roller, thus preventing the paper from being caught by the fixing roller.
The stripping finger which is used in the development section is not required to have resistance to a high temperature because the photosensitive drum is not required to be heated, but to have a sliding contact characteristic not to damage the photosensitive drum which is comparatively soft.
The stripping finger which is used in the fixing section is required to have resistance to a high temperature because the fixing roller has a heater inside it and thus the surface thereof is kept at a high temperature and in addition, property of preventing fused toner from sticking thereto.
The stripping finger disclosed in each of Laid-Open Japanese Patent Publication Nos. 5-173444 and 6-194989 is formed of a resin composition containing whisker and solid lubricant added to thermoplastic polyimide resin prepared from 4,4'-bis (3-aminophenoxy) biphenyl and pyromellitic dianhydride. The stripping finger disclosed in Laid-Open Japanese Patent Publication No. 5-107977 is formed of a resin composition containing thermotropic liquid crystal polymer to which a glass-like carbon is added.
In recent years, processing speed has become faster and compact and light weight electrophotographic apparatuses are manufactured. In addition, they are required to have a higher reliability. Thus, the fixing roller is required to withstand a high temperature and rotate at a high speed. Consequently, the stripping finger is required to have the following characteristics (1)-(5) for higher quality, higher reliability, and longer life.
(1) The stripping finger has a low frictional resistance to the peripheral surface of the fixing roller and does not have property of attacking the peripheral surface thereof. PA1 (2) The material of the stripping finger can be molded by injection and with high precision. PA1 (3) The stripping finger has property of preventing toner from sticking thereto or the material thereof can be treated to have property of preventing toner from sticking thereto. PA1 (4) The stripping finger has a high degree of heat load resistance, heat deformation property (more than 250.degree. C.), and heat fatigue resistance (more than 200.degree. C.). PA1 (5) The tip of the stripping finger has a high degree of heat load resistance and maintains its original shape reliably even when the stripping finger is used successively.
However, the conventional stripping finger formed by molding thermoplastic polyimide resin or liquid crystal polymer does not contain a sufficient amount of filler and solid lubricant which are required to allow the stripping finger to have superior mechanical strength and wear and friction characteristics. This is because the addition of the filler and the solid lubricant to the thermoplastic polyimide resin or the liquid crystal polymer leads to deterioration of the moldability of the thermoplastic polyimide resin or the liquid crystal polymer. Therefore, the conventional stripping finger does not have the above characteristics (1)-(5) required for them at a satisfactory level.